The present invention relates to light mixing and pertains particularly to sampling for color control feedback using an optical cable.
Light mixing is used to produce a desired color from base colors. For example red, green and blue (RGB) light emitting diodes (LEDs) can be used in a mixing cavity to produce a desired resultant color. A light mixing cavity is used to ensure thorough mixing of the RGB LEDs so that an eye will perceive the desired resultant color. If the mixing is incomplete, an eye may see different color spots on a surface of the mixing cavity.
There are many uses for a mixing cavity. For example, a mixing cavity with a suitable light guide panel can be used as a backlight for a liquid crystal display (LCD). In this case, thorough mixing of colors is very important to ensure color and brightness uniformity across the LCD. Typically, backlighting for an LCD requires one color point across all the display area. For example, the color point is a white D65 color point. A diffusant can be used across the surface of the mixing cavity to improve uniformity of color and brightness.
A mixing cavity can also be used, for example, to provide room lighting. In this case color mixing within a mixing cavity is not as crucial as in cases like providing backlighting for an LCD. A lens can be added to the surface of the mixing cavity to gather light and illuminate the room. In this case, it is usually not considered a defect if directly looking at the LED light source results in seeing red, green and/or blue spots so long as reflected light from all surfaces is able to diffuse the three color sources into one resultant color.
When using mixing cavities that require accurate mixing of colors, it may be desirable to obtain feedback about a produced color. This can be done, for example, using a light sensor placed within the light cavity. However, the brightness may cause saturation of the light sensor. Alternatively, a light sensor can be placed outside the light cavity; however, in this case, ambient light can sometimes impact the quality of the obtained color feedback.